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Tick-transmitted parasite could threaten blood supply

A new government-led study has found that the nation's blood supply is vulnerable to a tick-transmitted parasite that is widespread in parts of Minnesota and Wisconsin and seven Northeast states.

The report reviewed 159 cases of babesiosis that have been traced to blood transfusions during a 30-year period from 1979 to 2009. At least seven of the cases occurred in Minnesota, and two of those patients died.

Researchers say a rapid test is needed to screen donor blood for the parasite.

Babesiosis is a malaria-like illness transmitted to humans by the black-legged tick, also known as the deer tick. Babesia parasites typically invade their host as a result of a tick bite, but they can also be transmitted by blood transfusion.

That's a big concern for organizations like the American Red Cross because blood products that contain the parasite can be deadly to patients with weakened immune systems.

"We believe transfusion transmission of Babesia is still a relatively rare entity, but still definitely does occur," said Dr. David Mair, senior medical director of the Red Cross in St. Paul. "And since we don't have a licensed test yet to screen donors for Babesia, this makes it an issue."

The St. Paul Red Cross chapter has been collecting data on the prevalence of the parasite in blood donors. Researchers will test 2,000 participants in Minnesota and western Wisconsin for exposure to Babesia by the time the study wraps up this fall.

Mair said the current test would not be an appropriate way to screen large numbers of donors because it is time-consuming and expensive.

"Hopefully this will provide some preliminary information to get what the extent of the problem may be here in our donor base," he said. "And hopefully down the road, this may partially be able to contribute to the development of an automated test that could be able to be used to actually screen the blood supply for this agent."

Studies done in the northeastern United States show the presence of Babesia in about one percent of blood donors. Mair expects a similar rate of exposure in the upper Midwest. If the results are significantly higher than one percent of the population, it could result in more restrictions on the local blood supply, he said.

Blood donors who test positive for babesiosis are already barred from donating blood. But many donors may have no clue that they have ever been infected with the parasite. Most people who contract the disease have either no symptoms, or they experience a mild, flu-like illness that doesn't require medical treatment.

As it is not feasible to test every blood donor in the state for babesiosis, it's crucial that physicians watch their transfusion patients closely for signs of the disease, Minnesota Department of Health epidemiologist Melissa Kemperman said.

"There's a lot of people out there who need blood," Kemperman said. "So the last thing we want to do is tell people, 'Hey, if you've ever got a tick bite or ever spent time in the woods, don't give blood,' because then we'd be facing an emergency of not having enough blood."

Minnesota also has had two confirmed cases of anaplasmosis traced to blood transfusions. Anaplasmosis is a more common tick-borne disease, but Kemperman said it does not appear to be transmitted as easily through the blood supply as babesiosis.

There are more than 1,000 cases each year of Lyme disease, the most common tick-transmitted disease in Minnesota. So far the Minnesota Department of Health has seen no evidence that Lyme disease can be transmitted through blood transfusions.